you have two choices

1. make the sub menu you want to be default in sequence, by modifying the sequence on th sub menu item

2. identify the action of the sub menu on the root module menu

Hi Denny,

By default, Odoo will load the menu from the sequence wise. So you need to add the sequence as per the menu sequence you want.

In your case,  please add sequence=2 in the Restaurant Overview parent menu. and sequence=1 in the Report Dashboard  parent menu.

So by default when you install the Restaurant Overview module, the 2nd sequence menu will be load. and after installing Report Dashboard module, the fist menu will be the Report Dashboard because it's contain the prior sequence than other.

Hope it will help you.